How do you determine the appropriate degree of metal deformation in the forging process?

　　China Forging Talent Network: After punching, the dimensions of forged parts typically change—specifically, the height dimension tends to decrease, while the radial dimension increases.

　　The forging ratio is a measure of the degree of metal deformation during forging. It is expressed as the ratio of the cross-sectional area before and after the metal is deformed. Depending on the specific forging process, the method for calculating the forging ratio varies.

　　1. Drawing-to-Forging Ratio: The ratio of the cross-sectional area before drawing to the cross-sectional area after drawing

　　2. Upsetting Forging Ratio: The ratio of the cross-sectional area after upsetting to the cross-sectional area before upsetting

　　As the forging ratio increases, the internal porosity is compacted, and the as-cast dendritic structure is broken up, leading to a significant improvement in both the longitudinal and transverse mechanical properties of the forged component. However, once the drawing-to-diameter ratio exceeds 3–4, further increases in the forging ratio result in the development of pronounced fibrous textures, causing a sharp decline in the plasticity characteristics of the transverse direction and ultimately introducing anisotropy into the forged part. On the other hand, if the forging ratio is chosen too low, the component may fail to meet the required performance standards; conversely, selecting a ratio that’s too high not only increases the forging workload but also exacerbates anisotropy. Therefore, determining an optimal forging ratio is a critical issue, and it’s equally important to account for the problem of uneven deformation during the forging process.

　　The forging ratio is typically measured by the degree of deformation during lengthening. It refers to either the ratio of the original material's length to its diameter before shaping, or the ratio of the cross-sectional area of the raw material (or preform) before forging to that of the finished part after forging. The magnitude of the forging ratio significantly influences the mechanical properties of the metal and the quality of the forged component. Increasing the forging ratio generally helps refine the metal’s microstructure and enhance its performance—but excessively high ratios, however, offer no further benefits.

　　The principle for selecting the forging ratio is to choose a smaller value whenever possible, provided that all the requirements for the forged part are met. Generally, the forging ratio is determined based on the following criteria:

　　1. For high-quality carbon structural steel and alloy structural steel during free forging on a hammer: - For shaft-type forgings, when forged directly from steel ingots, the forging ratio calculated based on the main cross-section should be ≥3; when calculated based on flanges or other protruding features, the forging ratio should be ≥1.75. - If steel billets or rolled stock are used, the forging ratio calculated based on the main cross-section should still be ≥1.5, while for flanges or other protruding areas, it should remain ≥1.3. - For ring-type forgings, the typical forging ratio should be ≥3. - For disc-type forgings, when forged directly from steel ingots, the upsetting forging ratio must be ≥3. In all other cases, the upsetting forging ratio is generally required to be >3, though the final forging operation should exceed 2.

　　2. For high-alloy steel billets, it’s essential not only to eliminate structural defects but also to ensure a more uniform distribution of carbides throughout the material. This requires employing a significantly higher forging ratio. Typically, the forging ratio for stainless steel can be set between 4 and 6, while for high-speed steel, it should range from 5 to 12.